One way clutches used in automotive applications fall into two general categories, sprag clutches and roller clutches. Sprag clutches use the simplest clutch races, consisting of two completely cylindrical pathways, but the most complex wedging elements, consisting of asymmetrical, dumbbell shaped cams that drag along the surfaces during an overrun condition, but which jam between the races to lock up. The load that each cam, with its narrow waist, can sustain is limited, so a large number of them is necessary. Concentricity between the races is maintained by two bordering plain bearing end rings, generally bronze, which are axially retained by separate end rings. Complexity and cost of the clutch is therefore quite high.
A low cost alternative to the sprag clutch is the roller clutch, in which one of the races is more complex, but the wedging elements are far simpler, stronger, and less costly, costing of simple cylindrical rollers biased toward a wedging position by springs. An example may be seen in FIGS. 1 through 4. One of the clutch races, often (but not necessarily) the inner race 22, has a simple cylindrical pathway 32, as a sprag clutch would have. The other race 20 has a more complex shape, consisting of a regularly spaced series of semi cylindrical bearing surfaces 28 interspersed with saw tooth or wedge shaped cam ramps 24 and cam hooks 26. These together define what may be referred to as individual wedging spaces, as shown in FIG. 3, each of which is an imaginary four sided volume surrounding each spring-roller pair S-R. The circumferentially extending sides of each wedging space, indicated at A and B, represent an equal fraction of the total circumference of the annular space between the races 20 and 22. The axially extending sides of that four sided space, indicated at C and D, are defined by the pathway 32 and the individual bearing surfaces 28, which are radially spaced from pathway 32 by a consistent distance Rs, at least when races 20 and 22 are coaxial. Conversely, if the distance Rs is consistently maintained by some inserted structure, then the races 20 and 22 are maintained coaxial. This is exactly how roller clutches do maintain the races coaxial, by closely supporting the bearing surfaces on the pathway with semi cylindrical, solid, axially extending journal blocks.
Another important consideration with overrunning clutches of either type used in automotive applications is lubrication. It is important that the pathway be kept lubricated at the interface where it rubs on the end ring or journal block and on the sprag element or roller. An even more significant consideration with overrunning clutches used as passively acting shift speed matches in vehicle automatic transmissions is the ability to direct pressurized lubricant radially outwardly from and through the inner race, through the clutch, and through the outer race to cool a clutch disk pack splined to the outside of the outer race. It is necessary to either closely axially confine the pressurized lubricant between the axially spaced cage side rails of the clutch (i.e., to closely fill the axially spaced sides A and B of the wedging spaces), or to somehow route the lubricant completely around the roller clutch. Various past proposed mechanisms to so direct the pressurized lubricant may be seen in co-assigned U.S. Pat. Nos. 4,714,803; 4,782,931; 4,874,069; and 4,971,184. Briefly summarized, each of these provide additional structure used to confine or redirect lubricant, additional beyond the minimal elements necessary for the clutch cage itself. This, of course, adds cost and complexity that it would be advantageous to avoid.
A few known designs seek to combine sprag clutch type bearing end rings for concentricity control with caged cylindrical rollers as wedging elements. An example may be seen in U.S. Pat. No. 4,236,619. There, simple annular metal end rings 4 are shown bordering a plastic roller clutch cage, and acting as plain bearings to maintain concentricity. While it is recited that the end rings would prevent lubricant leakage, there is no structure disclosed that would block or prevent the end rings from simply being blown axially outwardly if high pressure oil were introduced between them. A later design in the same vein may be seen in U.S. Pat. No. 5,042,628. There, solid metal end rings 22 are formed with a series of outwardly projecting, small tabs 22d that are intended to snap fit into a dedicated circular groove machined into the pathway. This would provide more security against axial end ring blow out than the plain rings 4 of U.S. Pat. No. 4,236,619. However, since neither a solid metal end ring or integral tabs have much inherent flexibility, there is only a limited area of radial overlap (tab in groove) to provide retention. Moreover, pressurized oil could escape around the tabs 22d which, again, have a very limited area and would consequently provide very little blockage against escape.
A more recent design covered in co-assigned U.S. Pat. No. 5,632,720, shown in FIG. 4, takes a different approach. Concentricity control is done through close fitting journal blocks 48, but these, and the entire cage itself, are split into tow halves along a central plane so that each cage half can radially span the entire annular space between the races 20 and 22, and yet still be simply individually molded by an axial draw technique. By matching the shape of the outer edge of the cage side rails closely, all four sides of the wedging space as defined above can be almost solidly spanned and filled, providing both load support between the races (concentricity control), and a good measure of lubricant confinement. To retain the cage halves after installation, the inner ends of the journal blocks 48 are molded with barbs 54 at the end, and with axially extending slots 50, which give the two halves of the cage good flexibility. The barbs 54 snap into a center slot 30 in the cam race 20 when the cage is installed, although a special jig is needed to guide the cage into place.
An inherent drawback recognized in the above patent is the fact that the retention strength of the cage halves is limited by the degree of radial overlap between the narrow barbs 54 and the edges of the internal groove 30. Were the highly pressurized lubricant retained too completely between the cage side rails, they might, as a consequence, be blown axially outwardly, overcoming the retention strength of the barbs 54, or at least opening up a leak path at bowed out areas. Therefore, controlled leakage of lubricant outwardly through the groove 30 and slots 50 is deliberately provided for. In addition, it is inherently more difficult to shape match the convex saw-toothed edge of a cage side rail to the concave saw-tooth shape of a cam race, than to match a simple cylindrical bearing to a cylindrical pathway. Therefore, some radial clearance between the edge of the cage side rail 46 and the cam race's cam ramps 24 and cam hooks 26 is, as a practical matter, inevitable, which can also create a lubricant leak path. Close conformation between the race surfaces 32 and 28 and the journal blocks 48 would have to take preference over close conformation to the edges of the cage side rails 46, since lubricant leakage can be tolerated more easily than race eccentricity.